The present invention relates generally to a method for cleaning a plasma treatment system for carrying out the plasma treatment of a substrate to be treated, such as a semiconductor wafer, and a plasma treatment system.
Typically, an interconnection layer of aluminum is used as a metallization pattern of an integrated circuit, and an SiO2 or SiOF film is used as an interlayer insulator film for insulating the interconnection layer. As a method for depositing these layer and films, there is a tendency to use, e.g., the ECR (Electron Cyclotron Resonance) plasma treatment, which utilizes the combination of a microwave with a magnetic field, since the quality of films deposited by the method is good.
FIG. 28 shows an example of a plasma treatment system for carrying out the ECR plasma treatment. A microwave of, e.g., 2.45 GHz, is supplied into a plasma production chamber 1A via a waveguide 11. Simultaneously, a magnetic field of a predetermined magnitude, e.g., 875 gausses, is applied into the plasma production chamber 1A by means of an electromagnetic coil 121. Thus, the interaction (resonance) between the microwave and the magnetic field produces a plasma of a plasma gas, such as Ar or O2 gas, and a plasma of a reactive gas, such as SiH4 gas, which is introduced into a thin film deposition chamber 1B. These plasmas form an active species of SiH4 gas to deposit a thin film on the surface of a semiconductor waver W transferred onto a transfer table 13 of AlN (aluminum nitride).
In such a plasma treatment system, when the deposition treatment of an SiO2 film and so forth is carried out, these films are adhered to the side wall of the thin film deposition chamber 1B and the surrounding portion of the transfer table 13. When the thin film deposition treatment proceeds to allow the film to have a certain thickness, the adhered film is peeled off to cause particles. Therefore, after the deposition treatment of the SiO2 or SiOF film is carried out, a predetermined cleaning is carried out to remove the adhered film.
For example, the cleaning for removing the SiO2 or SiOF film is carried out for, e.g., about 20 minutes, each time the deposition on, e.g., 12 wafers W, is carried out. As a cleaning gas, a F containing gas, such as CF4 or NF3 gas, is introduced into a vacuum vessel, and this gas is activated by a plasma to allow the active species to react with the adhered film to remove the adhered film.
After the cleaning is completed, a predetermined precoat is carried out in order to prevent particles remaining on the inner wall of the vacuum vessel 10 from scattering and so forth. This precoat is a treatment for depositing a precoat film on the inner wall of the vacuum vessel 10. For example, in the case of the deposition treatment of an SiO2 film or the like, the precoat film is formed of an SiO2 or SiF4 film.
By the way, the SiO2 film has a dielectric constant of about 4, and the SiOF film has a dielectric constant of about 3.5. In recent years, a demand for higher speed devices has been raised, so that a demand for interlayer insulator films having a low dielectric constant has been made. Therefore, as such an interlayer insulator film having a low dielectric constant, a fluorine containing carbon film (which will be hereinafter referred to as a xe2x80x9cCF filmxe2x80x9d) capable of having a dielectric constant of 2.5 or less has been widely noticed.
This CF film can be also deposited by the above described plasma treatment system. However, if the F containing gas, such as CF4 or NF3 gas, is used to carry out the cleaning of the CF film, the cleaning hardly progresses when only CF4 gas is used. In addition, when only NF3 gas is used, the cleaning rate is very slow, and the treatment takes a long time, about 90 minutes. Thus, if the cleaning takes a long time, there is a problem in that the throughput in the thin film deposition treatment deteriorates since the cleaning is carried out during the thin film deposition treatment.
In addition, when the cleaning is carried out, the transfer table 13 is exposed to plasma. However, since the CF film is not originally adhered to the surface of the transfer table 13, the surface of the transfer table 13 is directly struck with plasma to become rough. Thus, when the surface of the transfer table 13 becomes rough, the surface of the transfer table has irregularities, so that the absorbing force onto the wafer W and the thermal conduction into the wafer Ware partially changed. In addition, the thin film deposition treatment changes between the initial and later stages of the process, so that the reproducibility of the process deteriorates. Therefore, there is a problem in that the inplane uniformity of the thickness of the deposited film deteriorates or the face-to-face uniformity of the thickness thereof deteriorates.
Moreover, if the surface of the transfer table 13 becomes rough, there are also problems in that the rough surface of the transfer table 13 may cause particles when the wafer W is loaded onto the transfer table 13 to carry out the subsequent thin film deposition treatment or unloaded from the transfer table 13, and that the life of the expensive transfer table 13 may be reduced. For example, when a particularly strong plasma is intended to be produced to increase the cleaning rate, there is a problem in that the surface of the transfer table deteriorates considerably.
In addition, when the cleaning is carried out, an operator observes the interior of the thin film deposition chamber 1B via a peep hole 14, which is formed in the side wall of the thin film deposition chamber 1B, to determine the finish time of the treatment by recognizing whether the film remains. According to such a method, the determination of the finish time may be incorrect since it is relied upon the experience of the operator. Consequently, there are problems in that the determined finish time is too early so that the film remains, and that in order to prevent the determination of the early finish time, the determined finish time is late so that the cleaning time is too long, thereby reducing the throughput in the thin film deposition treatment.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a method for cleaning a plasma treatment system, which can shorten the time required for the cleaning of a fluorine containing carbon film adhered in a vacuum vessel. It is another object of the present invention to provide a method for cleaning a plasma treatment system, which can protect a transfer table when the cleaning of an adhered film is carried out.
In addition, the CF film can be also deposited by means of the above described plasma treatment system. However, if the precoat film is formed of an SiO2 or SiOF film when the deposition treatment of the CF film is carried out, there is a problem in that the precoat film is easy to react with a raw material gas of the CF film, e.g., a CF gas, such as C4F8 gas, to produce particles, and the precoat used for the deposition treatment of the CF film has many unknown components.
It is therefore another object of the present invention to provide a plasma treatment method, which can carry out a stable thin film deposition on a substrate to be treated, by reducing particles in a vacuum vessel.
According to the present invention, a plasma treatment system cleaning method comprises: a thin film deposition step of transferring a substrate to be treated, onto a transfer table provided in a vacuum vessel, and producing a plasma of a thin film deposition gas to deposit a fluorine containing carbon film on the substrate by means of the plasma of the thin film deposition gas; and a cleaning step of producing a plasma of an oxygen plasma producing gas in the vacuum vessel, and removing the fluorine containing carbon film adhered in the vacuum vessel, by means of the plasma of the oxygen plasma producing gas. The plasma production of the thin film deposition gas may be carried out by producing the plasma of the thin film deposition gas by the interaction between a microwave and a magnetic field. In this case, the electric power of the microwave per unit volume (1 cubic meter) of the vacuum vessel is preferably set to be 10 kW or more.
Alternatively, the plasma production of the thin film deposition gas may be carried out by forming a magnetic field by a magnetic field forming means so that a line of magnetic force runs from a region, which faces a surface to be treated of a substrate to be treated, toward the substrate, and by producing a plasma of the thin film deposition gas on the basis of the interaction between an electric field and the magnetic field. In this case, the cleaning step is preferably carried out while adjusting the magnetic field so that the line of magnetic force near the substrate is more divergent than that in the thin film treatment step. Moreover, in this case, the magnetic field forming means may comprise a first coil, which is wound so as to surround a central axis of the substrate and which is provided above the substrate, and a second coil, which is wound so as to surround a central axis of the substrate and which is provided on a side of the substrate or below the substrate. The magnetic field adjustment is preferably carried out by causing a current flowing through the second coil to be smaller (including zero) than that when the plasma treatment carried out, or by causing a current flowing through the second coil to flow in a reverse direction.
In addition, when ac power is applied to an oxygen plasma producing gas to produce a plasma and when the fluorine containing carbon film is removed by this plasma, the cleaning step is preferably carried out while turning the ac power on and off by a pulse having a lower frequency than that of the ac power. The cleaning step may be carried out each time a thin film deposition treatment for one substrate to be treated is carried out.
The oxygen plasma producing gas is preferably selected from the group consisting of oxygen gas, a gas comprising oxygen gas and hydrogen gas, a gas comprising oxygen gas and a fluorine containing gas, a gas of a compound of oxygen and fluorine, water vapor, a gas of a compound of carbon and oxygen, and a gas of a compound of nitrogen and oxygen. The cleaning step may be carried out using an oxygen plasma producing gas comprising oxygen gas, and then, using an oxygen plasma producing gas comprising a gas of a compound of oxygen and fluorine.
Moreover, according to the present invention, the emission intensity at a specific wavelength emitted from a predetermined active species, which is produced in the vacuum vessel when the cleaning step is carried out, is preferably detected, and the finish time of the cleaning is preferably determined on the basis of the detected result.
According to the present invention, a plasma treatment method comprises: a thin film deposition step of transferring a substrate to be treated, onto a transfer table provided in a vacuum vessel, and producing a plasma of a thin film deposition gas to deposit a fluorine containing carbon film on the substrate by means of the plasma of the thin film deposition gas; a cleaning step of producing a plasma of a cleaning gas, and removing the fluorine containing carbon film adhered in the vacuum vessel, by means of the plasma of the oxygen plasma producing gas; and a pretreatment thin film deposition step of producing a plasma of a pretreatment thin film deposition gas, and forming a thin film for preventing particles from being produced, such as a fluorine containing carbon film or an amorphous carbon hydride film, on an inner wall of the vacuum vessel by means of the plasma of the pretreatment thin film deposition gas. The pretreatment thin film deposition gas for depositing the fluorine containing carbon film may be a gas containing a compound of carbon and fluorine, the compound having a double bond or a triple bond.